Electroplating processes and compositions

ABSTRACT

THIS INVENTION RELATES TO A PROCESS AND COMPOSITION FOR THE PREPARATION OF AN ELECTRODEPOSIT WHICH CONTAINS AT LEAST ONE METAL SELECTED FROM THE GROUP CONSISTING OF NICKEL AND COBALT AND WHICH ALSO MAY CONTAIN IRON, WHICH COMPRISES PASSING CURRENT FROM AN ANODE TO A CATHODE THROUGH AN AQUEOUS PLATING SOLUTION CONTAINING AT LEAST ONE MEMBER SELECTED FROM THE GROUP CONSISTING OF COBALT COMPOUNDS AND NICKEL COMPOUNDS AND WHICH MAY ALSO CONTAIN IRON COMPOUNDS TO PROVIDE COBALT, NICKEL AND FERROUS IONS FOR ELECTRODEPOSITING COBALT, NICKEL NICKEL-COBALT ALLOYS, NICKEL-IRON ALLOYS, OR NICKEL-COBALT-IRON ALLOYS THE IMPROVEMENT COMPRISING THE PRESENCE OF AN EFFECTIVE AMOUNT OF BORIC ACID AND AT LEAST ONE MEMBER SELECTED FROM THE GROUP CONSISTING OF MANNITOL, SORBITOL, AND DULCITOL IN A SINGLE OR COMBINED CONCENTRATION OF 2 GRAMS PER LITER TO 100 GRAMS PER LITER FOR A TIME PERIOD SUFFICIENT TO FORM A SOUND METAL ELECTROPLATE UPON SAID CATHODE SURFACE.

United States Patent 3,804,726 ELECTROPLATING PROCESSES AND COMPOSITIONSFrank Passal, Detroit, Mich, assignor to M & T Chemicals Inc.,Greenwich, Conn. No Drawing. Filed April 23, 1973, Ser. No. 353,310 Int.Cl. C23h 5/08, 5/32, 5/46 US. Cl. 204-43 T 23 Claims ABSTRACT OF THEDISCLOSURE This invention relates to a process and composition for thepreparation of an electrodeposit which contains at least one metalselected from the group consisting of nickel and cobalt and which alsomay contain iron, which comprises passing current from an anode to acathode through an aqueous plating solution containing at least onemember selected from the group consisting of cobalt compounds and nickelcompounds and which may also contain iron compounds to provide cobalt,nickel and ferrous ions for electrodepositing cobalt, nickel,nickel-cobalt alloys, nickel-iron alloys, or nickel-cobalt-iron alloysthe improvement comprising the presence of an effective amount of boricacid and at least one member selected from the group consisting ofmannitol, sorbitol, and dulcitol in a single or combined concentrationof 2 grams per liter to 100 grams per liter for a time period suflicientto form a sound metal electroplate upon said cathode surface.

This invention relates to improved processes and compositions for theelectrodeposition of nickel, cobalt, and alloys one with another andwith iron. More particularly, this invention relates to the use of newadditives to improve the buffering capacity of nickel, cobalt, and alloyplating baths containing nickel and/or cobalt and to facilitating theplating of iron-containing alloys of nickel, cobalt, and nickel-cobalt.

BACKGROUND OF THE INVENTION One of the most serious problems withcommercial nickel plating is the precipitation of basic ferric saltswith the main sources of iron being as an impurity in the nickel anodematerials used, from solution attack on ferrous basis metal parts beingplated, from chemicals used for bath makeup and replenishment and fromtap water used to replenish water lost by evaporation at the usualplating bath temperatures. When these basic ferric salts precipitate,particularly when pH values of about 3.8 electrometric or higher arereached, they tend to clog anode bags which interferes with freecirculation of solution between anode and cathode compartments leadingto partial anode polarization (resulting in liberation of oxygen orchlorine or both which attack and decompose organic additives thusadversely affecting performance and increasing operating costs). Theprecipitate also tends to clog filter media thereby markedly slowingdown rates of filtration; this results in frequent and expensive filtercleaning and repacking, and also may result in inferior quality ofdeposits due to particle roughness, etc. If the concentration of thesuspended precipitate in the bath reaches too high a value theprecipitate may be electrophoretically codeposited with the nickelresulting in pitting, dull grainy areas, etc., particularly on shelf"areas.

In the electrodeposition of nickel, cobalt or nickel cobalt from avariety of electroplating baths the anode current efliciency underaverage operating conditions is about 100%. The cathode efliciency,however, is about 95% resulting in evolution of hydrogen at the cathodethereby resulting in the increase in hydroxyl (OH-) ion content in thebath which causes an increase in bath pH. If the pH exceeds an optimumrange, say 3.8 to 4.2 for semi-bright or bright-nickel plating orelectroforming ap-, plications, the limiting current density may bedecreased i.e. the current density at the cathode where burnt orpowdery, unsound deposits may be produced, especially on high curentdensity edges or corners or projections of articles being plated. Thisnecessitates periodic, and under high volume plating, rather frequentadditions of an appropriate acid, such as sulfuric or hydrochloric orsulfamic acid, to lower the pH to a value within optimum limits.

Where anode area is not adequately maintained or where excessively highcurrents per unit volume are used the anodes may partially polarizeresulting in evoluiton at the anode of oxygen or chlorine (fromchloride-com taining baths) or both. It is thus possible, therefore,that the anode current efiiciency may be lower than the cathodeetficiency thereby resulting in an accumulation of excess hydrogen ions(H'*) in the bath resulting in a tendency toward decreasing pH to avalue below optimum limits. Under such circumstances not only will theanodically evolved 0 or C1 tend to decompose organic bath additives toadversely affect plating characteristics such as deposit luster etc. butthe pH must be periodically increased to a value within recommendedlimits. Since this necessitates the addition, generally, of a carbonateof the metal or metals being plated, or of a hydroxide or carbonate orbicarbonate of a bath compatible cation, such as Na or Ca or Sr or Ba,and since these materials are either sparingly soluble or slowlyreactive or may cause localized precipitation of basic nickel salts theyobviously cannot be added directly to the plating bath during operation.The usual modus operandi is to add one or more of these materials inincremental portions in the filter which is rather inconvenient since itinvolves the use of a filter feed special attachment andwhich may bealso troublesome since it may disturb the filter cake (filteraid+activated carbon etc.) and introduce particles into the plating bathwhich may cause roughness of electrodeposits. It would therefore behighly desirable to modify the bath composition so as to increase thebulfering capacity of the bath so as to counteract in some significantdegree a tendency either for rising or falling pH. The usually addedboric acid does help to buffer the cathode film i.e. the thin layer ofsolution immediately adjacent to the cathode, but it provides ratherpoor buffering action for the body of the plating bath.

A bath which is particularly sensitive to pH is one for platingsemi-bright or bright cobalt involving the use of one or more organicadditives. If the. pH becomes too high i.e. in the range of 3.8 to 4.2or higher there is a strong tendency toward obtaining unsightly andunsatisfactory nonuniform, brownish, stained deposits in the highcurrent density end of the range.

It is an object of this invention to improve the bufferingcharacteristics and thereby the pH stability of baths for theelectrodeposition of semi-bright or bright nickel, cobalt, alloys ofnickel and cobalt, alloys of nickel and iron and alloys ofnickel-cobaltiron. A special object of this invention is to provideprocesses and compositions for the production of sound electrodepositscontaining nickel and/or cobalt and iron over a wide range ofconcentrations of additives without substantial precipitation of basicferric salts. Other objects of the invention will be apparent from thefollowing detailed description of the invention.

DETAILED DESCRIPTION In accordance with certain of its aspects, thisinvention relates to a process for the preparation of an electrodepositwhich contains at least one metal selected from the group consisting ofnickel and cobalt and which may also contain iron, which comprisespassing current from an anode to a cathode through an aqueous platingsolution containing at least one member selected from the groupconsisting of cobalt compounds, nickel compound, and which may alsocontain iron compounds to provide cobalt, nickel and iron ions forelectro-depositing cobalt or nickel, or alloys of both and also ironalloys of each or both, the improvement comprising the presence of 2grams per liter to 100 grams per liter, in single or combinedconcentration, of at least one member selected from the group consistingof mannitol, sorbitol, and dulcitol for a time period sufi'lcient toform a sound metal electroplate upon said cathode surface. Mannitol,sorbitol and dulcitol are optical isomers having the following formula:

HOCH (CHOH) CH OH The baths may contain an effective amount of at leastone member selected from the group consisting of:

(a) primary brightener (b) secondary brightener (c) secondary auxiliarybrightener (d) anti-pitting agent The substrates on which thenickel-containing, cobaltcontaining, nickel-cobalt-containing,nickel-iron-containing or nickel-cobalt-iron containing electrodepositsof this invention may be applied may be metal or metal alloys such asare commonly electrodeposited and used in the art of electroplating suchas nickel, cobalt, nickel-cobalt, copper, tin, brass, etc. Other typicalsubstrate basis metals from which articles to be plated are manufacturedmay include ferrous metals such as steel; copper; tin and alloys thereofsuch as with lead; alloys of copper such as brass, bronze, etc.; zinc,particularly in the form of zinc-base die castings; all of which maybear plates of other metals, such as copper, etc. Basis metal substratesmay have a variety of surface finishes depending on the final appearancedesired, which in turn depends on such factors as luster, brilliance,leveling, thickness, etc. of the cobalt, nickel, or iron containingelectroplate applied on such substrates. 7

The term primary brightener" as used herein is meant to include platingadditive compounds such as reaction products of epoxides withalpha-hydroxy acetylenic alcohols such as diethoxylated 2butyne-l,4-dio1 or dipropoxylated 2 butyne-l,4-diol, other acetylenics,N- heterocyclics, active sulfur compounds, dye-stuffs, etc. Specificexamples of such plating additives are:

1,4-di- (fl-hydroxyethoxy)-2-butyne 1,4di- (B-hydroxy-y-chloroprop oxy)-2-butyne 1,4-di-(fi-,'y-epoxypropoxy)-2-butyne 1,4-di- (fi-hydroxy--butenoxy)-2-butyne 1,4-di-(2'-hydroxy-4'-oxa-6'-heptenoxy)-2-butyneN-1,2-dichloropropenyl pyridinium chloride 2-butyne-1,4-diol /CH:CH2CN]CHzCHzCN fuchsin posits. However, best results are obtained when primarybrighteners are used with either a secondary brightener,

a secondary auxiliary brightener, or both in order to provide optimumdeposit luster, rate of brightening, leveling, bright plate currentdensity range, low current density coverage, etc.

The term secondary brightener as used herein is meant to includearomatic sulfonates, sulfonamides, sulfonimides, sulfinates, etc.Specific examples of such plating additives are:

(l) saccharin (2) trisodium l,3,6-napthalene trisulfonate (3) sodiumbenzene monosulfonate (4) dibenzene sulfonimide (5 sodium benzenemonosulfinate Such plating additive compounds, which may be used singlyor in suitable combinations, have one or more of the followingfunctions:

(1) To obtain semi-lustrous deposits or to produce substantialgrain-refinement over the usual dull, matte, grainy, non-reflectivedeposits from additive free baths.

(2) To act as ductilizing agents when used in combination with otheradditives such as primary brighteners.

(3) To control internal stress of deposits, generally by making thestress desirably compressive.

(4) To introduce controlled sulfur contents into the electrodeposits todesirably afiect chemical reactivity, potential ditfernces in compositecoating systems, etc. thereby decreasing corrosion, better protectingthe basis metal from corrosion, etc.

The term secondary auxiliary brightener as used herein is meant toinclude aliphatic or aromatic-aliphatic olefinically or acetylenicallyunsaturated sulfonates, sulfonamides, or sulfonimides, etc. Specificexamples of such plating additives are:

( 1) sodium allyl snlfonate (2) sodium-3-chloro-2-butene-l-sulfonate (3)sodium fl-styrene sulfonate (4) sodium propargyl sulfonate (5) monoallylsulfamide (H NSO NHCH CH=CH (6) diallyl sulfamide NH-Allyl [02S :l

NH-Allyl (7) allyl sulfonamide Such compounds, which may be used singly(usual) or in combination have all of the functions given for thesecondary brighteners and in addition may have one or more of thefollowing functions:

(1) They may act to prevent or minimize pitting (probably acting ashydrogen acceptors).

(2) They may cooperate with one or more secondary brighteners and one ormore primary brighteners to give much better rates of brightening andleveling than would be possible to attain with any one or any twocompounds selected from all three of the classes:

(1) primary brightener;

(2) secondary brightener; and

(3) secondary auxiliary brightener used either alone or in combination;

(3) They may condition the cathode surface by catacooperating additives(usually of the primary brightener type) may be substantially reduced,making for better economy of operation and control.

Among the secondary auxiliary brighteners one may also include ions orcompounds of certain metals and metalloids such as zinc, cadmium,selenium, etc. which, although they are not generally used at present,have been use to augment deposit luster, etc. Other cooperatingadditives of Organic nature which may be useful are the hy- 5 droxysulfonate compounds of US. Pat. No. 3,697,391 i.e. typically, sodiumformaldehyde bisulfite, the function of which is to make baths moretolerant to primary brightener concentrations, to increase tolerancetoward metallic impurities such as zinc, etc.

The term anti-pitting agent as used herein is meant to include amaterial (different from and in addition to the secondary auxiliarybrightener) which functions to prevent or minimize gas pitting. Ananti-pitting agent may also function to make the baths more compatiblewith contaminants such as oil, grease, etc. by their emulsifying,dispersing, solubilizing, etc. action on such contaminants and therebypromote attaining of sounder deposits. Anti-pitting agents are optionaladditives which may or may not be used in combination with one or moremembers selected from the group consisting of a primary brightener, asecondary brightener, and a secondary auxiliary brightener. Preferredanti-pitting agents may include sodium lauryl sulfate, sodium laurylether sulfate and sodium di-alkylsulfosuccinates.

Typical nickel-containing, cobalt-containing, andnickelcobalt-containing bath compositions which may be used incombination with effective amounts of about 2 grams per liter to 100grams per liter of the mannitol, sorbitol, or dulcitol compounds andelfective amounts of about 01005-02 grams per liter of the primarybrighteners, with about 1.0-30 grams per liter of the secondarybrightener, with about 05-10 grams per liter of the secondary auxiliarybrightener, and with about 0.05-1 gram per liter of anti-pitting agent,described herein are summarized below.

Typical aqueous nickel-containing electroplating baths (which may beused in combination with effective amounts of cooperating additives)include the following wherein all concentrations are in grams per liter(g./l.) unless otherwise indicated:

TABLE I.-AQ,UEOUS NICKEL-CONTAINING ELECTRO- PLATING BATES MinimumMaximum Preferred Component:

- Nickel sulfate 200 500 300 Nickel chloride 30 80 45 Boric acid-.." 3555 45 pH (eleetromet 3 5 4 When ferrous sulfate (FeS .7H O) is includedin the foregoing bath the concentration is about 5 grams per liter to 80grams per liter.

A typical sulfamate-type nickel plating bath which may be used inpractice of this invention may include the following components:

When ferrous sulfate (FeS0 .7H O) is included in the foregoing bath theconcentration is about 5 grams per liter to 80 grams per liter.

vA typical chloride-free sulfate-type nickel plating bath which may beused in practice of this invention may include the following components:

TABLE III Minimum Maximum Preferred When ferrous sulfate (FeSO .7H O) isincluded in the foregoing baths the concentration is about 5 grams perliter to grams per liter.

It will be apparent that the above baths may contain compounds inamounts falling outside the preferred minimum and maximum set forth, butmost satisfactory and economical operation may normally be effected whenthe compounds are present in the baths in the amounts indicated. Aparticular advantage of the chloride-free baths of Tables III and IV,supra, is that the deposits obtained may be substantially free oftensile stress and may permit high speed plating involving the use ofhigh speed anodes.

The following are aqueous cobalt-containing and c0-balt-nickel-containing electroplating baths in which the combination ofeffective amounts of one or more cooperating additives according to thisinvention will result in beneficial AQUEOUS COBALT-CONTAINING ANDCOBALT-NICKEL- CONTAINING ELEOTROPLA'IING BATES [All concentrations ing./l. unless otherwise noted] Maximum Minimum Preferred V. Cobalt bath:

00804-7 H20 400 200 300 COC12-6 1120---- 75 15 60 113303.; 50 37 45 VI.Cobalt bath:

00804 7 20 500 300 400 N 2101 50 15 3O HsBOam 50 37 45 VII. Highchloride cobalt bath:

C0 z-fi z 500 200 I 300 HaBOa 50 37 I 45 X. Suliamate cobalt bath: 7 p

00(O2SNH2)2 400 200 290 CoCh-fi H2O.-

When ferrous sulfate (FeSO .7.H O) is included in the foregoing bathsthe concentration is about 5 grams per liter to 80 grams per liter.

Preferred cobalt-containing bath compositions may contain at least about30 g./l. of CoCl .6H O, and typically, 2*0-50 g./l. of CoCl .6H O. Othercompounds which have abath compatible cation (i.e. a cation which doesnotinterfere with the operation of the bath) which will provide at least7.5 g./l. of chloride ion, Cl- (and preferably a minimum of about 9g./l. of C) may also be used.

The pH of all of the foregoing illustrative aqueous nickel-containing,cobalt-containing, nickel-cobalt-containing, andvnickel-cobalt-iron-containing compositions may be maintained duringplating at pH values of 2.5 to 5.0, and preferably from about 3.0 to4.0. During bath operation, the pH may normally tend to rise and may beadjusted with acids such as hydrochloric acid or sulfuric acid, etc.

Operating temperature ranges for the above baths may be about 30 to 70C. with temperatures within the range of 45 to 65 C. preferred.

Agitation of the above baths during plating may consist of solutionpumping, moving cathode rod, air agitation or combinations thereof. Forapplications involving the deposition of alloys containing iron frombaths in which the iron is predominantly in the ferrous (divalent) stateof valency, it is preferable to use very mild agitation i.e. movingcathode rod, to minimize air oxidation of ferrous to ferric iron.

Anodes used in the above baths may consist of the particular singlemetal being plated at the cathode such as nickel or cobalt for platingnickel or cobalt respectively. For plating binary or ternary alloys suchas nickel-cobalt, nickel-iron or nickel-cobalt-iron, the anodes mayconsist of the separate metals involved suitably suspended in the bathas bars, strips or small chunks in titanium baskets. In such cases theratio of the separate metal anode areas is adjusted to correspond to theparticular cathode alloy composition desired. For plating binary orternary alloys one may also use as anodes alloys of the metals involvedin such a percent weight ratio of the separate metals as to correspondto the percent weight ratio of the same metals in the cathode alloydeposits desired. These two types of anode systems will generally resultin a fairly constant bath metal ion concentration for the respectivemetals. If with fixed metal ratio alloy anodes there does occur somebath ion imbalance, occasional adjustments may be made by adding theappropriate corrective concentration of the individual metal salts. Allanodes are usually suitably covered with cloth or plastic bags ofdesired porosity to minimize introduction into the bath of metalparticles, anode slime, etc. which may migrate to the cathode eithermechanically or electrophoretically to give roughness in cathodedeposits.

The following examples are submitted for the purpose of illustrationonly and are not to be construed as limiting the scope of the inventionin any way.

EXAMPLE 1 A nickel electroplating bath composition was prepared bycombining in water the following ingredients to provide the indicatedconcentrations (in g./l. unless indicated otherwise).

A polished brass panel was scribed with a horizontal single pass of 2/0grit emery to give a band width of about 1 cm. at a distance of about2.5 cm. from the bottom of the panel. After cleaning the panel,including the use of a thin cyanide copper strike to assure excellentphysical and chemical cleanliness, it was plated in a 267 ml. Hull Cell,at a 2 ampere cell current for minutes, at a temperature of 50 C. andusing magnetic stirring. The resulting deposit was uniformlyfine-grained, glossy in appearance, with excellent ductility and a veryslight uniform background haze. The leveling was only fair.

On adding to the solution 2.3 =g./l. of sodium allyl sulfonate andrepeating the plating test the resulting deposit was brighter andslightly better leveled as evidenced by the degree of obliteration orfilling in of the emery scratches. I

On further adding to the solution of 50 mg./l. of 1,4-di-(fi-hydroxyethoxy)-2-butyne a brilliant, well-leveled, ductiledeposit with slight tensile stress and excellent low current densitycoverage was obtained.

EXAMPLE 2 Example 1 was repeated using as the acetylenic primarybrightener, 1,4-di-(,B-hydroxypropoxy)-2-butyne in place of1,4-di-(,s-hydroxyethoxy)-2-butyne and essentially the same results wereobtained.

EXAMPLE 3 Example 1 was repeated using as a primary brightener 20 mg./l.of N-allyl-quinaldinium bromide as a replacement for1,4-di-(fi-hydroxyethoxy)-2-butyne and essentially the same results wereobtained except that the degree of leveling was not as high.

EXAMPLE 4 A nickel-cobalt-iron electroplating bath was prepared as inExample 1 but containing only 40 g./l. of ferrous sulfateand inaddition, containing 40 g./l. of cobalt sulfate heptahydrate (CoSO -7HO). The plating test sequence of Example 1 was then repeated withessentially the same results obtained.

EXAMPLE 5 EXAMPLE 6 A bath was prepared having the followingconcentration of salts to give atypical high chloride type bath:

I G./l. Nickel chloride 200 Nickel sulfate 50 Boric acid 40 Sorbitol 36The additives of Example 1 were used in the sequence given in Example 1and the ferrous sulfate was added in increments. Highly lustrous,ductile deposits having fair degree of leveling were obtained up to aferrous sulfate concentration of about 50 g./l. Higher concentrations offerrous sulfate resulted in partial milky, partially thin striated,non-uniform deposits indicating an upper limit to the useable ferrousiron content.

- EXAMPLE 7 The bath of Example 1 was then subjected to a 4 liter lifetest using conditions as follows:

Plating cell-5 liter rectangular cross-section (13 cm. x 15 cm.) made ofPyrex.

Solution volume-4 liters to give a solution depth, in absence of anode,of about 20.5 cm.

Temperature55 C. (maintained by immersing cell in a thermostaticallycontrolled water bath).

Agitation-moving cathode rod.

Anode--single bagged titanium basket containing SD nickel squares.

Cathode-brass strip (2.54 cm. x 0.071 cm.) buffed and polished on oneside and immersed to a depth of about 17.8 cm.horizontal bend 2.54 cm.from bottom and the next 2.54 cm. bent to give an internal angle on thepolished side of cathode of about 45 polished side facing anode at anapproximate distance of 10.2 cm. and scribed vertically in center with a1 cm. wide band of a single pass of 2/0 grit emery paper scratches.

Cell current5.0 amperes.

Timesolution electrolyzed about 7 hours per day occasional cathodesplated for 30 minutes to evaluate deposit leveling, uniformity,ductility, luster (overall and in low current density recessed area).

Filtration-occasional batch.

Additions-the pH was periodically adjusted when necessary with dilutesulfuric acid to within a range of 3.0 to 3.5 electrometric; periodicreplenishment additions of the primary brightener and the secondaryauxiliary brightener were made to maintain deposit luster and leveling.The ferrous iron content of the bath was maintained with separate nickeland Armco iron anode systems in bagged titanium baskets with occasionalcorrective additions of ferrous sulfate, based on analysis for ferrousiron, to maintain the nickel and ferrous iron contents of the bathfairly constant.

The life test was run in excess of 1125 ampere-hours per 4 liters usinga ampere cell current. Although a small amount of basic ferric saltprecipitate formed its amount was small enough to be commerciallyhandled and removed by continuous filtration. The main source of thisbasic ferric salt precipitate was its formation on the anode bags; thebody of the solution remained quite clear. A typical deposit was platedfor one hour on a stainless steel substrate to give a brilliant,relatively ductile, well-leveled deposit which was stripped off thesubstrate and analyzed. The deposit was found to contain about 50% byweight Ni and about 50% by weight Fe.

The deposits have the following general characteristics:

Brightness-very good and easy to maintain. Ductility-Excellent.

Internal stress-40w tensile.

Levelingfairly good (about same as bright cobalt). Hydrogenembrittlement by chromium plating-livery low. Pitting tendency-very low.

Smoothness of depositsexcellent.

EXAMPLE 8 Example 7 was repeated using a bath without sorbitol. Within arelatively short electrolysis time of several hours the bath assumed amuddy appearance on stirring due to formation of basic ferric salts.This condition manifested itself in the appearance of the deposits whichshowed micro-roughness and orange-peel and even a haze or dullness onshelf areas of the bent cathodes where the basic salt precipitateaccumulated to a greater degree. This condition became progressivelyworse and the bath had to be taken out of operation at the end of about1 65 ampere-hours of electrolysis.

The solution was then filtered and 36 g./l. of sorbitol were added. Inthe place of the electrolytic nickel squares in a titanium basket usedin previous tests there were suspended in the bath an elliptical crosssection rolled depolarized anode containing carbon. On resuming theelectrolysis excellent deposits were obtained for about 195 additionalampere-hours at the end of which electrolysis the deposits began to showpartial dull graininess. During this second electrolysis the anode hadformed a dark film of carbon. It was suspected that the change inplating characteristics had occurred due to partial anode polarizationresulting in build up of ferric iron in excessive concentration. Thiswas confirmed by analysis which showed the presence in solution of 3.5g./l. of ferric iron. The remarkable factor was that even with thisrelatively high ferric iron content the bath had remained perfectlyclear and free of basic iron precipitate although at the bottom of thecontainer there was some accumulation of anode carbon flakes. Due to thesoluble ferric iron which could impart a yellow color the solution hadchanged from a clear transparent green to a dark olive green in colorand was opaque in appearance.

The pH of the solution was then adjusted to 3.0 electrometric and thesolution was stirred at 140 F. with 40 grams of pure iron powder for 30minutes. At the end of this period the solution was again clear greendue to the reduction of ferric to ferrous iron by the iron powder. Afterfiltration to remove the iron powder the bath was set up forelectrolysis again, now using a bagged titanium basket containingelectrolytic nickel squares (which apparently resist polarization betterthan rolled depolarized carbonized nickel with the mild agitation used)and the baths excellent plating characteristics were again restored.This sequence of tests indisputably proved the remarkable complexing andsolubilizing effect of sor- 10 bitol on ferric iron under conditionswhere it would normally precipitate out as a basic salt.

There are two ways in which the buffering characteristics of a nickel,cobalt, or nickel-cobalt plating bath may be evaluated and these are thefollowing:

(1) Taking a known volume of plating bath and adjusting the pH to somerelatively low value. While stirring the bath, in which there isimmersed a glass electrode-calomel electrode system connected to a pHmeter to monitor pH, a solution of an alkali such as saturated sodiumbicarbonate, is added in small increments and, after achievingequilibrium after each increment, the pH is read. This results in aseries of pH readings and volume of alkali additions which may beplotted on rectangular coordinate graph paper as ordinates and abscissarespectively to give a buffering curve for the system. The greater thevolume of alkali solutions required to change the pH from one value toanother, say pH 2.0 to 5.0, the greater is the buffering capacity of thesystem. A 'visual indication of buffering capacity as produced by someadidtive (say mannitol, sorbitol. dulcitol) is the more rapid flatteningout of the buffer curve, i.e., it becomes more nearly parallel with theabscissa.

(2) To electrolyze a bath containing no buffering improvement additiveand one containing a buffering improvement additive, preferably inseries, the solutions having equal volumes and operated at the sametemperature, cell current, anode area, agitation, etc. The amount ofacid required to readjust the pH to the starting value periodically forthe two baths is then compared. The lower the acid consumption thehigher is the degree of buffering capacity.

The following examples illustrate method 1 using as the plating bath aWatts type nickel plating bath having the following makeup composition:

G./l. Nickel sulfate 300 Nickel chloride 60 Boric acid 45 EXAMPLE 9 Noadditive Ml. sat. Na-HCO pH electrometric EXAMPLE 10 25 g./l. sorbitol 11 EXAMPLE -Continued Ml. sat. NaHCO pH electrometric EXAMPLE 11 25 g./l.dulcitol Ml. sat. NaHCO pH electrometric 0 1.70 2.5 1.85 5.0 2.00 7.52.35 10.0 3.20 12.5 3.75 15.0 4.10 17.5 4.30 20.0 4.50 22.5 4.70 25.04.80 27.5 4.90 30.0 0.05 35.5 5.20

EXAMPLE 12 25 g./l. mannitol Ml. sat. Nail-I00 pH electrometric 0 1.652.5 1.80 5.0 2.00 7.5 2.35 10.0 2.85 12.5 3.25 15.0 3.55 17.5 3.85 20.03.95 22.5 4.10 25.0 4.30 27.5 4.45 30.0 4.60 32.5 4.70 35.0 4.80 37.54.90 40.0 5.00

The following example shows that inositol which is C H (OH) or1,2,3,4,5,6 cyclohexane hexol does not impart the degree of buiferingcapacity of the three compounds of this invention, viz. manitol,sorbitol, and dulcitol.

EXAMPLE 13 25 g./l. inositol 12 Ml. sat. NaHCO pH 17.5 4.95 20.0 5.1022.5 5.20

To summarize Examples 9 to 13 inclusive in terms of ml. of sat. NaHCOrequired to raise the pH from 2 to 5 the following can be calculated:

Ml. 1) No additive 14 (2) Sorbitol 25 (3) Dulcitol 25 (4) Mannitol 35(5) Inositol 12.5

. G./l. Cobalt sulfate 300 Cobalt chloride 60 Boric acid 45 EXAMPLE 14No additive Ml. sat. NaHCO pH 0 1.60 1 1.65 3 1.85 6 3.10 8 4.05 9 4.3010 4.40 11 4.50 12 4.60 14 4.70 16 4.80 18 4.90 20 5.00

EXAMPLE 15 25 g./l. sorbitol Ml. sat. NaHCO pH 0 1.65 1 1.70 3 1.75 62.20 8 2.70 10 3.20 12 3.50 14 3.75 16 3.95 18 4.15 20 4.30 22 4.45 244.55 26 4.70 28 4.80 30 4.85 33 5.00 36 5.10 40 5.25

It can be seen from Examples 14 and 15 that to increase the pH from 2 to5 there are required about 16 ml. Without additive and about 29 ml. for25 g./l. sorbitol respectively indicating the pronounced increase inbuffering capacity produced by sorbitol.

13 To illustrate the beneficial effects of sorbitol on a sulfamate typenickel plating bath as used commonly for electroforming the followingexamples are given:

G./l. Nickel sulfamate 375 Nickel chloride 6 Boric acid 37.5

EXAMPLE 16 No additive Ml. sat. NaHCO pH 1.65 1 1.70 2 1.75 3 1.80 51.85 7 2.00 10 2.15 12.5 2.35 15.0 2.85 18.0 4.05 20.0 4.40 22.0 4.5525.0 4.85 30.0 4.95- 35.0 5.10

EXAMPLE 17 25 g./l. sorbitol Ml. sat. NaHCO pH 0 1.65 1 1.70 2 1.75 51.80 10 2.05 12.5 2.20 15.0 2.45 20 3.20 22.5 3.60 3.80 28 4.10 30 4.254.50 4.75 4.95 5.05

It may be seen from Examples 16 and 17 that it required in going from pH2 to 5 about 23 ml. with no additive and about 40 ml. with 25 g./l.sorbitol.

EXAMPLE 18 A 4-liter life test was run using the following conditions:

Plating cell-5 liter rectangular cross-section (13 cm. x 16 cm.) made ofPyrex.

Solution volume--4 liters to give a solution depth, in absence of anode,of about 20.5 cm.

Temperature- C. (maintained by immersing cell in a thermostaticallycontrolled water bath).

Agitation-filtered air through a glass and polyethylene s ider.

Anode---single bagged titanium basket containing electrolytic nickelsquares.

Cathode-brass strip (2.54 cm. x 20.3 cm. x 0.071 cm.) buffered andpolished on one side and immersed to a depth of about 17.8cm.-horizontal bend 2.54 cm. from bottom and the next 2.54 cm. bent togive an internal angle on the polished side of cathode of about 45polished side facing anode at an approximate distance of 10.2 cm. andscribed vertically in center with a 1 cm. wide band of a single pass of2/0 grit emery paper scratches.

Cell current-5 .0 amperes.

Time--solution electrolyzed about 7 hours per day-- occasional cathodesplated for 30 minutes to evaluate deposit leveling, uniformity,ductility, luster (overall and in low current density recessed area).

The bath composition was as follows:

Nickel sulfate g /l 300 Nickel chloride g./l 60 Boric acid g./l 45Sorbitol g /1 25 pH, 4.0 electrometric. Sodium saccharinate (0.6H 0)g./l 3.2 Sodium allyl sulfonate ..g./l-.. 2.3 Dipropoxylated 2butyne-1,4-diol m'g./l 50 Sodium di-n-hexylsulfosuccinate g./l 0.25

The above solution was operated for a total of 670 ampere-hours withperiodic replenishment of organic additives. Early in the life test itwas found that the pH stabilized at a value of about 4.3 and this pH wasallowed to remain at this value except that on two widely sepa rateddays a small amount, less than 5 ml., of 1-1 connoticed in depositappearance or phsyical properties indicating that besides stabilizing pHsorbitol was essentially inert in its action on bath performance.Mannitol and dulcitol would produce essentially the same effect.Sorbitol would be preferred for commercial large scale use because ofits ready availablity and substantially lower cost than mannitol anddulcitol.

Although this invention has been illustrated by reference to specificembodiments, modifications thereof which are clearly within the scope ofthe invention will be apparent to those skilled in the art.

I claim:

1. In a process for the preparation of an electrodeposit which containsat least one metal selected from the group consisting of nickel andcobalt, and which may also contain iron, which comprises passing currentfrom an anode to a cathode through an aqueous acidic plating solutioncontaining at least one member selected from the group consisting ofnickel compounds, cobalt compounds, and ferrous compounds providing ionsfor electrodepositing nickel, cobalt, nickel-cobalt alloys, nickelironalloy, or nickel-cobalt-iron alloy, the improvement comprising thepresence of boric acid and at least one compound selected from the groupconsisting of mannitol, sorbitol, and dulcitol in single or combinedconcentration of 2 grams per liter to grams per liter.

2. The process of claim 1 wherein said nickel compounds are nickelsulfate and nickel chloride.

3. The process of claim 1 wherein said nickel compounds are nickelsulfamate and nickel chloride.

4. The process of claim 1 wherein said cobalt compounds are cobaltsulfate and cobalt chloride.

5. The process of claim 1 wherein said cobalt compounds are cobaltsulfamate and cobalt chloride.

6. The process of claim 1 wherein said ferrous compound is ferroussulfate or ferrous chloride.

7. A. process for the preparation of an iron alloy electrodeposit whichcontains at least one metal selected from the group consisting of nickeland cobalt which comprises passing current from an anode to a cathodethrough an aqueous acidic plating solution containing boric acid,ferrous sulfate, or ferrous chloride, and at least one member selectedfrom the group consisting of cobalt compounds and nickel compoundsproviding cobalt and/or nickel ions for electrodepositin'g cobalt and/ornickel and iron containing in combination an effective amount of:

15 (l) at least one member selected from the group of cooperatingadditives consisting of:

(a) primary brightener (b) secondary brightener (c) secondary auxiliarybrightener and (d) anti-pitting agent; and (2) grams per liter to 50grams per liter in single or combined concentration of at least onemember of the group consisting of mannitol, sorbitol, and dulcitol;

for a time period sufiicient to form a sound metal electroplate uponsaid cathode surface.

8. The process of claim 7 wherein said nickel compounds are nickelsulfate and nickel chloride.

9. The process of claim 7 wherein said cooperating additives are sodiumsaccharinate, sodium allyl sulfonate, 1,4-di-(p-hydroxyethoxy)-2-butyne,and sodium lauryl sulfate.

10. The process of claim 7 wherein said cooperating additives are sodiumsaccharinate, sodium allyl sulfonate,1,4-di-(B-hydroxypropoxy)-2-butyne, and sodium lauryl sulfate.

11. In a process for the preparation of an electrodeposit which containsat least one metal selected from the group consisting of nickel andcobalt which comprises passing current from an anode to a cathodethrough an aqueous acidic plating solution containing at least onemember selected from the group consisting of nickel compounds and cobaltcompounds, the improvement comprising the presence of boric acid and atleast one member selected from the group consisting of mannitol,sorbitol, and dulcitol in a single or combined concentration of 2 gramsper liter to 100 grams per liter.

12. The process of claim 11 wherein said nickel compounds and saidcobalt compounds are nickel and cobalt sulfates, sulfamates, andchlorides.

13. In an aqueous acidic electroplating solution containing at least onemember selected from the group consisting of nickel compounds, cobaltcompounds, and ferrous compounds, providing ions for electrodepositingnickel, cobalt, nickel-cobalt alloy, nickel-iron alloy, ornickel-cobalt-iron alloy, the improvement comprising the presence ofboric acid and at least one compound selected from the group consistingof mannitol, sorbitol, and dulcitol in single or combined concentrationof 10 grams per liter to 50 grams per liter.

14. The composition as claimed in claim 13 wherein said nickel compoundsare nickel sulfate and nickel chloride.

15. The composition as claimed in claim 13 wherein said nickel compoundsare nickel sulfamate and nickel chloride.

16. The composition as claimed in claim 13 wherein said cobalt compoundsare cobalt sulfate and cobalt chloride.

17. The composition as claimed in claim 13 wherein said cobalt compoundsare cobalt sulfamate and cobalt chloride.

18. The composition as claimed in claim 13 wherein said ferrous compoundis ferrous sulfate or ferrous chloride.

19. An aqueous acidic electroplating solution which contains boric acid,ferrous sulfate or ferrous chloride, and at least one member selectedfrom the group consisting of cobalt compounds and nickel compoundsproviding cobalt and/or nickel ions for electrodepositing cobalt and/ornickel and iron containing in combination an effective amount of:

(1) at least one member selected from the group of cooperating additivesconsisting of:

(a) primary brightener (b) secondary brightener (c) secondary auxiliarybrightener and (d) anti-pittting agent; and

(2) 10 grams per liter to grams per liter in single or combinedconcentration of at least one member of the group consisting ofmannitol, sorbitol, and dulcitol.

20. The composition of claim 19 wherein said nickel compounds are nickelsulfate and nickel chloride.

21. The composition of claim 19 wherein said cooperating additives aresodium saccharinate, sodium allyl sulfonate,1,4-di-(fl-hydroxyethoxy)-2-butyne, and sodium lauryl sulfate.

22. The composition of claim 19 wherein said cooperating additives aresodium saccharinate, sodium allyl sulfonate, 1,4 di(p-hydroxypropoxy)-2-butyne, and sodium lauryl sulfate.

23. In an aqueous acidic electroplating solution containing at least onemember selected from the group consisting of nickel compounds and cobaltcompounds, the improvement comprising the presence of boric acid and atleast one member selected from the group consisting of mannitol,sorbitol, and dulcitol in single or combined concentration of 2 gramsper liter to 100 grams per liter.

References Cited UNITED STATES PATENTS 3,677,912 7/1972 Passal 204-493,697,391 10/1972 Passal 204-43 T GERALD L. KAPLAN, Primary Examiner US.Cl. X.R. 204-48, 49

